The present invention relates to the field of image sensors.
Backside illuminated semiconductor photo-diode image sensors are known in the art; see for example U.S. Pat. No. 5,494,833 to Martin et al. Front-illuminated charged-coupled device (CCD) image sensors have demonstrated good performance in the visible and near IR portions of the spectrum. However, losses due to optical absorption in the polysilicon CCD gates cause moderate degeneration in quantum efficiency in the visible and severe degradation in the blue and UV portions of the spectrum. Back illuminated configurations have been used to reduce these losses,; however, an improved process for making back illuminated CCD image sensors is desired that provides near reflection limited UV quantum efficiency, together with excellent stability under UV exposure. Thinned, UV sensitive backside illuminated CCD image sensors have been fabricated by the inventors by means of high temperature processing steps necessary to produce the desired electric field and electrically passivated surfaces to return the best response for such a backside illuminated image sensor. Such procedures were referred to in a general fashion only in an M.I.T. Lincoln Laboratory Solid State Research Quarterly Technology Report of Jul. 30, 1993.